A multi-step procedure is often used to introduce electrical stimulation leads, catheters, probes or the like into a body vessel, most notably into the vascular system, typically the venous system. Generally this procedure consists of inserting a hollow needle into a blood vessel, such as the subclavian vein. A wire guide is then passed through the needle into the interior portion of the vessel. The needle is then withdrawn and an introducer sheath and dilator assembly is then inserted over the wire guide into the vessel. The assembly is advanced into a suitable position within the vessel, i.e. so that the distal end is well within the vessel but the proximal end is outside the patient. Next, the dilator and wire guide are removed from the introducer sheath lumen. The introducer sheath is left in position and therefore offers direct access from outside the patient into the blood vessel lumen. Then, a lead, catheter or the like can be passed through the introducer sheath lumen into the blood vessel lumen and ultimately be positioned in a desired site, e.g., within the patient's selected heart chamber or an associated blood vessel.
Such a system and method is commonly employed for percutaneously introducing pacing leads for permanent or temporary pacemakers or arrhythmia control devices. In the implantable pacemaker context, an implantable pulse generator is electrically connected to the heart by at least one pacing lead, e.g. an endocardial lead introduced transvenously. More specifically, an endocardial lead provides an electrical pathway between the pacemaker pulse generator, connected to the proximal end of the lead, and endocardial tissue, in contact with one or more electrode at the distal end of the lead. Endocardial tissue refers to a specific layer of tissue in the interior of the heart's chambers. In such a manner, electrical pacing pulses emitted by the pacemaker travel through the endocardial lead conductor and depolarize the endocardial tissue of the heart in contact with the electrode(s). The contraction of the heart is effected by the propagation of the evoked depolarization.
Endocardial pacing leads are often placed in contact with the endocardial tissue by passage through a venous access, such as the subclavian vein or one of its tributaries. In such a manner, transvenous endocardial leads offer as an advantage that they may be placed into contact with the heart without requiring major thoracic surgery. Rather, once the transvenous endocardial leads are introduced into a vein and maneuvered therefrom into contact with the heart, the vein access may be closed and the lead connector end may be tunnelled under the skin to the implant site of the pulse generator and attached thereto.
Such pacemaker leads typically have a relatively bulky connector pin assembly at the proximal end, and the introducer sheath is removed from the lead body at the end of the procedure by being split apart. In such a manner, the introducer sheath does not have to be removed over the relatively bulky connector pin assembly at the proximal end of the lead body.
One purpose of this well known procedure is to expand the lumen of the blood vessel accessed at the puncture site so that it can receive the distal end of the lead. The distal tip of the dilator is tapered to expand the blood vessel lumen as it is advanced through it. After the dilator is withdrawn, the sheath maintains the expansion of the blood vessel lumen and provides an introducer lumen for the distal end and body of the lead.
A problem exists in pacemaker patients who have had multiple leads implanted over time. Scar tissue at the site of lead introduction into a blood vessel during implantation has been found to create difficulties with past lead introduction systems. Specifically the relatively tough scar tissue hinders the introduction of a dilator and introducer sheath assembly. Many times, only through use of larger incisions than are otherwise desirable is such an assembly able to be inserted and advanced.
To provide such access under the best of circumstances, the introducer sheath must be flexible in order to permit the introducer sheath to bend and conform with blood vessel curves and bends. After placement in the vessel lumen, the introducer sheath end is substantially parallel to the blood vessel lumen, and a lead which is introduced therethrough is properly aligned with the vessel lumen. If the sheath did not conform to the vessel shape, a lead introduced through its distal end opening would abut against the vessel wall, possibly injuring the vessel wall and damaging the lead.
When an irregularity or scar tissue impediment to advancement of the assembly is encountered, it is necessary to remove the assembly from the incision into the blood vessel and to explore the reasons for it. One approach is to inject a radiopaque dye or contrast medium into the blood vessel lumen and observe it under fluoroscopy to identify any blockage sites, vessel wall perforations, scar tissue or other impediments to advancement. It may be that none are observable, and the procedure is repeated either with the same or with a different combination of dilator and introducer sheath. The same problem may be repeated. Even if blockage sites, perforations or other impediments are observed, the exact relation of the problem with the distal end portion of the assembly cannot be observed because it is no longer in place.
Since the guide wire lumen of the dilator is available, the physician may attempt to inject the dye or contrast media through it alongside the guide wire. It is difficult or not possible to pressurize the injection of the dye or contrast media and it also escapes back out the proximal end opening of the guide wire lumen of the dilator.